1. Field of the Invention
The present invention relates generally to a semiconductor device and, more particularly, to a lead-on-chip (LOC) where leads are laid out on a semiconductor chip.
2. Description of the Background Art
FIG. 6 is a perspective view illustrating a semiconductor device based on a conventional lead-on-chip structure, and FIG. 7 is a cross-sectional view of a simplified structure of FIG. 6. This semiconductor device is constructed so that inner leads 2a, 2b, 3a, 3b are bonded onto an upper surface of a chip 1 by use of bonding adhesive. A plurality of bonding pads 5 are arranged substantially in one row at the central portion of the upper surface of the chip 1. The inner leads 2a, 2b are used as lines for supplying power. The inner leads 2a, 2b extend in an arranging direction of the plurality of bonding pads 5 at the central portion of the chip 1, with the plurality of bonding pads 5 interposed therebetween. The inner leads 3a, 3b are employed as signal lines for transferring signals and each extend outwardly of the inner leads 11a, 11b. These inner leads 2a, 2b, 3a, 3b are connected at inner ends thereof via bonding wires 20, 22 to the bonding pads 5 corresponding thereto. Accordingly, the bonding wires 22 through which the inner leads 3a, 3b are connected to the bonding pads 5 are, as illustrated in FIG. 7, extended astride of the inner leads 2a, 2b for the power supply lines.
An insulating layer 25 is provided between the inner leads 2a, 2b and 3a, 3b. Thus constructed semiconductor device is normally molded with a resin to form a resin mold body 30. Lead portions projected from this resin mold body 30 are called outer leads 4.
According to the semiconductor device based on the above-mentioned lead-on-chip (hereinafter abbreviated to LOC) structure, there is no necessity for providing, outside the chip, the lead parts 2a, 2b, 3a, 3b for connecting the bonding wires led from the pads 5 on the chip 1. This therefore yields such an advantage that large-sized chip having its chip size approximate to a package size can be packaged.
As shown in FIG. 7, however, the bonding wires 22 for connecting the inner leads 3a, 3b to the pad 5 is extended astride of the power supplying inner leads 2a, 2b. It is therefore required that distance b between the bonding wire 22 and the inner leads 2a, 2b be made sufficiently in consideration of a deformation of the bonding wire 22 during the resin molding. It is also required that a distance between the bonding wire 22 and a molded resin boundary be made not to extrude the bonding wire 22 out of the resin. Under such circumstances, the conventional semiconductor device shown in FIGS. 6 and 7 presents a defect of being unsuited to a package having a small thickness of the resin because of the necessity for having a sufficient resin thickness (a+b) above the power supplying inner leads 2a, 2b.